Process utilizing carbon disulfide in aqueous emulsion polymerization of fluorinated monoolefins



3,043,823 PROCESS UTILIZING CARBON DISULFIDE IN AQUEOUS EMULSIONPOLYMERIZATION F FLUORINATED MONOOLEFINS Russell M. Mantel], Princeton,N.J., and John M. Hoyt, Cincinnati, Ohio, assignors to Minnesota Miningand Manufacturing Company, St. Paul, Minn., a corporation of Delaware NoDrawing. Filed Aug. 18, 1958, Ser. No. 755,417 7 Claims. (Cl. 260-92.1)

This invention relates to a process for the polymerization ofmono-olefins in aqueous media. In one aspect it relates to the emulsionpolymerization of fluorinecontaining olefins such aschlorotrifluoroethylene using a fluorocarbon dispersing agent.

The advantages of polymerizing mono-olefins in aqueous dispersions arewell known. However, until recently, it has not been possible topolymerize mono-olefins, particularly halogenated mono-olefins such astetrafiuoroethylene and chlorotrifluoroethylene, in fine dispersions,due to the fact that satisfactory dispersing agents are unknown.

It has recently been suggested that stable aqueous colloidal dispersionsof polymerized halogenated monoolefins could be prepared by polymerizingthe fluorinated monomer in the presence of aliphatic fluorocarbon acidsand salts. However, it was desirable to find a method for increasing theproduct yield.

It has now been found that the addition of carbon disulfide to thepolymerization system increases the rate of reaction as well as theoverall product yield. This novel process is especially noteworthybecause, contrary to expectations, the addition of carbon disulfide doesnot inhibit the polymerization, as is the rule with sulfides,mercaptans, ethers, alcohols, etc.

It is therefore an object of this invention to provide a process for thepolymerization of mono-olefins in aqueous media to produce a polymericproduct in high yields.

It is a further object of this invention to provide an improved processfor polymerizing fluorinated olefins, in an aqueous medium, such processproviding polymer in high yields.

Still another object of this invention is to provide an improved processfor polymerizing fluorinated olefins in aqueous medium, such processhaving a high reaction rate.

It is a further object of this invention to provide a fluid stable latexof chlorotrifluoroethylene polymer which can be applied directly for thecasting of strong flexible selfsupporting films, or for the coating ofmetal or other surfaces and for the impregnation of fibrous materials.

Other objects and advantages will become apparent from the descriptionand disclosure of the invention.

These and other objects are accomplished by polymerizing a mono-olefin,particularly a halogenated monoolefin whichis at least half fluorinatedand which con tains from 2' to 5, preferably from 23 carbon atoms, in anaqueous medium which contains carbon disulfide and a dispersing agent.When the mono-olefin is fluorinated, the preferred dispersing agents arealiphatic halocarbon acids, particularly aliphatic fluorocarbon acids,

such as produced by hydrolyzing a telomer of chlorotrifluoroethylene, ora water-soluble inorganic salt of such an acid, to produce a solid highmolecular weight polymerization product in the form of a dispersion.

Acids produced from chlorotrifluoroethylene telomers by hydrolysis maybe represented by the generic formula wherein n is an integer from 2 to16 and wherein Z is a mono-functional radical of the group consisting ofa per 3,043,323 Patented July 10, 1962 wherein n is an integer from 2 to16, preferably from 3-6, may be prepared in a specific example bydissolving 3.5 parts of benzoyl peroxide in 408 parts ofbromotrichloromethane and charging this solution to a pressure vesselalong with 300 parts of chlorotrifiuoroethylene. The system is heatedfor about four hours at about C. with agitation to produce high yieldsof relatively low molecular weight polymers having the above formula.These polymers may be distilled to produce individual compounds of theabove formula wherein n is a particular integer. The mixed polymer, orany fraction thereof, is treated with fuming sulfuric acid containingless than about 20% excess sulfur trioxide at a temperature betweenabout C. and about 175 C. for a period of time between about 10 hoursand 25 hours to produce monocarboxylic acids having an odd number ofcarbon atoms in the aliphatic chain with the structure A detaileddescription of this method of preparing perfiuorochloro. acids may befound in U.S. Patent No. 2,806,865.

Still another suitable perfluorochloro acid may be prepared by thetreatment with fuming sulfuric acid of a sulfuryl chloride telomer ofohlorotrifiuoroethylene; this telomer having the formula Cl(CF CFCl)--Cl, wherein n is an integer from 2 to 16, preferably from 3-6, may beprepared in a specific example by dissolving 3.5 parts of benzoylperoxide in 308 parts of carbon tetrachloride and parts of sulfiurylchloride, adding 116 parts of chlorotrifiuoroethylene and heating atabout 95 C. for a period of four hours. The telomers may be distilled toindividual compounds wherein n is a particular integer. The mixedtelomer, or any fraction thereof, is treated with fuming sulfuric acidcontaining from 0 to 20% excess sulfur trioxide at a temperature betweenabout C. to about 210 C. for a period of time ranging from 5 to 25 hoursto produce monocarboxylic acids of the formula A detailed description ofthis method of producing periluorochloro acids may be found in U.S.Patent No. 2,806,866.

In addition to the acids, alkali metal, such as sodium, potassium, etc.and amine and ammonium salts of the above acids may also be used.

Other suitable halocarbon acids include polyfluoroalkanoic acids of theformula H(CF -COOH and of the formula =F(CF ),,COOH and their alkalimetal, ammonium, amine or quaternary ammonium salts. Still otherfluorochloro acid salts dispersing agents within the scope of thisinvention may also be prepared by thermal cracking ofpolychlorotrifluoroethylene, as described in the copending applicationof David B. Brandon, Serial No. 452,704, filed August 27, 1954.

Mono-olefinic compounds which are Within the scope of this inventioncontain from 2 to 5 carbon atoms, preferably 2 to 3 carbon atoms, andinclude vinyl chloride, ethylene, proplyene, vinyl acetate, etc. Thefluorinated mono-olefins which constitute the preferred embodiment ofthis invention contain from 2 to 5 carbon atoms, preferably 2 to 3carbon atoms. Those mono-olefins which contain at least 50% of fluorinesubstitution are particularly preferred. The mono-olefinic monomerswithin the scope of this invention may be either homopolymerized orcopolymerized. Among the specific monomers which may be homopolymerizedare tetrafluoroethylene, chlorotrifluoroethylene, and vinylidenefluoride. Those that may be copolymerized in accordance with thisinvention include the above and additionally dichlorodifluoroethylene(symmetrical and unsymmetrical), perfiuoropropene, tri- Ichlorofluoroethylene, etc., any of Which may be copolymerized With eachother or with another halogenated olefin. The invention is particularlyuseful in the homopolymerization of chlorotrifluoroethylene to produce ahigh molecular weight plastic with a high no strength temperature, suchas 250 and above. This invention is also useful in the copolymerizationof chlorotrifiuoroethylene and vinylidene fluoride to produce resins andelastomers and in the copolymerization of perfiuoropropene andvinylidene fluoride to produce resins and elastomers.

The polymerization of monomers in accordance with this inventionrequires an aqueous medium, a dispersing agent of the class discussedabove, carbon disulfide, and a polymerization initiator, such as awater-soluble inorganic polymerization initiator, e.g. the ammonium andalkali metal persulfates, perborate or percarbonates, or an organicperoxide, such as cumene hydroperoxide. The preferred polymerizationinitiators or promoters are ammonium persulfate and alkali metalpersulfates, particu-, larly sodium or potassium persulfate. However, itis also within the scope of this invention to use ultraviolet light andother free radical formers as the initiator.

When polymerization is carried out at low temperatures, as preferredwhen homopolymerizing chlorotrifluoroethylene to a resin of high nostrength temperature, it may be desirable, though not necessary, toinclude, in

addition to the aforesaid polymerization initiator, a reductant such asammonium or Water-soluble alkali metal salt of a readily oxidizablesulfoXy compound, such as sodium sulfite, sodium bisulfite, sodiumthiosulfate and sodium hydrosulfite. In addition,it may also bedesirable, though not necessary, when polymerizing at low temperatures,below about 50C., to include a small amount of a Water-soluble salt of ametal capable of change of valence, as, fore example, a silver, copperor ferrous salt, such as ferrous sulfate. The polymerization medium mayalso include buffers such as borax, disodium phosphate, ammoniumcarbonate or sodium acetate. It is a particularly preferred embodiment,however, to omit both the reductant and the metal salt, as their usetends to discolor the product.

The polymerization process of this invention is preferably carried outat high pH, such as pH 7-14, preferably at a pH of about 8-11, and attemperatures from about to 100 C. usually about 15-35 C., for solidpolymers. The polymerization temperatures can be varied within the aboverange depending on the molecular Weight of the product desired.Pressures used are preferably autogenous and may go as high as 50atmospheres. With carbon disulfide used as an activator the control ofpH Within the above ranges is essential if the full effect of the carbondisulfide on the yield is to be obtained.

The concentration of mono-olefin in the aqueous dispersion may vary fromabout to about 50 percent by weight of the water present. The dispersingagent may be present in concentrations from about 0.1% to about 6percent by weight of the water present. The polymerization initiator orpromoter may be present in concentrations from about 001% to about 5%,based on the weight of monomer used., The amount of carbon di- Dry Ice.

sulfide used can vary from 1-50 parts by weight of monomer, thepreferred range being between about 5 and about 25 parts by weight ofmonomer. The salt of the variable valence metal is usually present, whenused, in an amount to provide from 0.2 to 600 parts per million offerrous ions based on the weight of the aqueous medium; and thereductant, when used, is usually present in an amount from 1 to 6 partsby weight per parts of total monomer, usually in equal amounts with thepromoter.

Polymerization generally takes place over a period of time ranging from20 minutes to 100 hours and produces high conversions of up to 100% ofthe monomer feed. When used in accordance with this invention, thepresence of carbon disulfide in the polymerization system greatlyenhances the overall conversion to the polymeric product.

The dispersions of the present invention may be stored as such or, ifdesired, the polymer produced may be recovered therefrom by coagulatingby rapid cooling or freezing, such as with a Dry Ice-acetone bath, or bycoagulating with a strong mineral acid, such as hydrochloric acid orsulfuric acid, or with a salt solution such as sodium or magnesiumchloride or aluminum sulfate, and then filtering, washing and drying. ByWashing with a suitable solvent the carbon disulfide can be removed fromthe polymer.

Another particular advantage of the high yield product dispersionsobtained by the method of this invention is that the latex product maystill be used directly as a coating dispersion, since the carbondisulfide volatilizes off at film forming temperatures. Thus theaddition of the carbon disulfide does not in any way alter thecharacteristics of the coating or film. This is particularlyadvantageous where such coating is subjected to severe conditions oftemperature and chemical attack. Applications for such polymers andlatices of such polymers, particularly the fluorinated polymers, is wellknown in the art and need not therefore be further mentioned here.

The following examples are offered to illustrate the invention and arenot to be construed necessarily as limiting its scope.

EXAMPLE .1

Emulsion polymerization of trifluorochloroethylene was conducted insealed 250 ml. glass polymerization tubes at 25 C. for 20 hours withshaking, using the following emulsion recipe:

CF 1=OFCl gm 41.2 2.5 wgt. percent aqueous solution of K S O ml 400 4.0wgt. percent aqueous solution of I Cl(CF OFCl) CF COOI-I alkalized to pH9-10 with KOH ml 46.8 5.25 wgt. percent aqueous solution of Na HPO ;7H Oml 38.2

At the completion of the 20 hours the sealed tubes were vented and thepolymer coagulated by rapid cooling in The coagulate was then filteredon a Biichner filter and washed with hot water until free from soapbubbles, after which the washed coagulate was vacuum dried over night at70 C. and about 100 mm. Hg pressure. Trifiuorochloroethylene polymer wasproduced in a 60% yield with a dilute solution viscosity of about 1.3cs. (0.75 Wgt. percent solution in dichlorobenzotrifluoride at 266 F.).

The above experiment was repeated with the addition of 4.2 grams of CSto the emulsion recipe. The resulting trifluorochloroethylene polymerhad a ZST (zero strength time) of about seconds and a dilute solutionviscosity (0.75% solution in dichlorobenzotrifluoride at 266 F.) ofabout 0.90 cs. A yield of 95% was produced, indicating the effect ofcarbon disulfide addition to the polymerization recipe. No sulfur couldbe detected in the polymer by the usual bomb combustion-barium sulfateanalysis.

EXAMPLE 2 Five recipes as shown in Table I were sealed in glass ampulesand shaken at 25 C. for 7 hours. After venting the ampules each polymersample was coagulated by rapid cooling in a Dry Ice-actone bath andfiltered with a sintered Biichner filter, the filtrates being collectedfor further testing. Each coagulate or precipitated polymer was wettedwith 50-75 cc. of methanol, and 100-300 cc. of distilled water wasadded, after which the liquid was drawn through the coagulate bysuction. This washing procedure was repeated nine times. A final washwith methanol completed the wash operation. The precipitates were vacuumoven dried in glass dishes at 70 C. and about 100 mm. Hg pressure over aperiod of 24 hours and then weighed. Test results on the originalfiltrate and yield data appear in Table II.

Table I 2.5 weight 4.0 Weight 5.25 weight CS2, OF2= percent percentpercent Run N 0. gm. CF01, gm. aqueous aqueous aqueous solution,solution, solution, ml. ml; ml.

41. 2 40 46. 8 38. 2 41. 2 40 46.8 38. 2 41. 2 40 46. 8 38. 2 41. 2 40 d46.8 38.2 41. 2 4O d 46. 8 38. 2

1 0.75 weight percent solution in dichlorobenzotrifluoride at 266 F. 2No strength temperature. 3 M1 0.1 N thiosuliate to equivalence for 5 ml.aliquot.

Surface tension was determined on the Du Nuoy tensiometer, the pH byusing a Beckrnan pH meter with a r glass reference electrode, and thefinal S O concentration by adding excess KI to a 5.0 mol aliquot andtitrating with 0.1 N thiosulfate solution to the starch-iodideequivalence point.

From the results obtained in the above runs it was concluded that theaddition of CS causes no detectable change in pH, surface tension, or 80 concentration in the filtrate. However, the yields of B and C, whichcontain CS were 54% and 69% higher than A, which contained no CS Aneight gram sample of polymer from each of runs A, B, and C was coldpressed at 5,000 p.s.i., then at 220- 230 C. and 5,000 p.s.i. andquenched. Clear, bubble free sheets resulted, thesamples from each ofthe runs being indistinguishable in transparency, appearance, andflexibility.

Samples D and B were polymerized without the use of a fluorinated acidsalt. Sample D contained CS while sample E contained no CS The percentyields, both with and without CS are low in the absence of thefluorinated acid salt.

6 EXAMPLE 3 Four samples as shown in Table III were sealed in glassampules and shaken at 25 C. for 7 hours.

After venting the ampules each polymer sample was coagulated by freezingin a Dry Ice-acetone bath, filtered and dried, as in Example 2. Theresults of the polymerization appear in Table IV.

Table III 2.5 4.0 5.25 weight weight weight Run NaOCN, CS2, OF=CFCLpercent percent percent No. gm. N 212C 03 gm. gm. aqueous aqueousaqueous solusolusolution, tion) tion,

A 41. 2 40 46. 8 38.2 B 0.4 41.2 40 46.8 38.2 0. 4 4.2 41.2 40 46.8 38.2 D 0.4 4. 2 41.2 40 46. 8 38.2

I KzSzOs. 01(CF2CFCD3CF2COOH alkalized with KOH to pH 9-10.NazHPo4-7Hzo.

Table IV Weight polymer Dilute pH of final Run N o. solution polymerviscosity, latex Gm Percent eentistokes 1 1 0.75 weight percent solutionin dichlorobenzotrifluoride at 266 F.

EXAMPLE 4 A polymerization run was, carried out in a 3 gallon horizontalautoclave using carbon disulfide in the polymerization recipe. 36 gramsof K S O and 72 grams of Na HPO .7H O were each dissolved in 1000 ml.quantities of distilled water. To 9.5 grams of KOH dissolved in 500 ml.of distilled water was added 67.5 gms. of C telomer acid, 'i.e. Cl(CFCFCl) CF COOH, with stirring The above prepared solutions were thenwashed into a polyethylene container with 2000 ml. of distilled waterand stirred. The resultant solution, having a pH of 8.6, was added tothe autoclave along with 150 grams of CS CF2-=CFC1 monomer (1286 gm.)was pressured into autoclave with nitrogen. Polymerization conditionswere continued at 22.825.5 C. for 24 /2 hours under autogenous pressure(-85 p.s.i.g.), after which the polymer latex (1.11 gm./ml., pH7.65,18.3% solids) was coagulated by freezing. The coagulate polymer waswashed three times by decantationwith cold water, three times bydecantation with hot water, and finally five times with hot water on afiltering funnel. The filtrate from the last wash was free of Cl(OFCFCl) CF COOH, as indicated by its failure to form a precipitate on theaddition of a solution of S-benzyl iso-thio-uronium chloride. Therecovered polymer, after being dried at C. for 16 hours, weighed 796grams, corresponding to a 62% conversion and a 72.5% yield aftercorrection for recovered monomer. Final polymer had a dilute solutionviscosity (0.75% soln dichlorobenzotrifluoride @266 F.) of 1.252 cs. anda ZST (zero strength time) at 260 C. of 317 sec.

When the above run was duplicated (20 hrs. at 23.5- 245 C.) withoutcarbon disulfide the polymer was realized in a conversion of 44.5%. Thispolymer had a ZST (260 C.) of 503 sec. and a DSV of 1.523 cs.

EXAMPLE 5 Using the same procedure described in Example 4, a

polymerization run was made in the 3 gallon horizontal autoclave usingthe following emulsion recipe:

8 We claim: 1. In a process for polymerizing a monomer charge consistingof at least one polymerizable fiuorinated ter monolefin having from 2 to5 carbon atoms at a tern- CS2 gm 150 5 perature between 0 and 100 C. 1nthe presence of K35208v gm 36 a polymerizatlon imtiator and m an aqueousmedium NaZHPOJHZO 72 havinga pH from 7 to about 14 and having afiuo-rinated G8 telomer acid "gm" 675 dispersing agent, the improvementwhich comprises add- Na CO gm 15 0 mg carbon disulfide to said aqueousmedium in an I 2 3 u 1O amount between 1 and 50 parts by weight per 100parts The pH of the initial combined charge was 9.90. After monomercharge. polymerization for 21 /2 hours at 7579 F. and autoge- 2. Theprocess of claim 1 in which the fluorinated nous pressure (120-92p.s.i.g.), the pH was 7.50 and the dispersing agent is selected from thegroup consisting polymer latex contained 1924% solids (1.12 gm./ml.) ofaliphatic fluorohalocarbon acids and the inorganic or 958.7 grns. ofpolymer. The conversion (based on 15 salts thereof. total monomer) was67% and the yield was 79.5% (cor- 3. The process of claim 1 in whichsaid aqueous rected for recovered monomer). The trifiuorochloromediumalso contains below about 10% by weight, based ethylene polymer, afterbeing dried at 150 C. for 48 on said carbon disulfide, of a mem er f theg p conhours, had a dilute solution viscosity of 1.230 es. and a Sistingof sodium carbonate and sodium cyanate ZST at 260 C f 332 sec 20 d 4.The process of claim 1 in which said aqueous meium a so contains belowabout 10% by wei ht, based EXAMPLE 6 on said carbon disulfide, of sodiumcyanate. g The polymerization runs in this group were performed 5. Theprocess of claim 1 in which said monomer in glass tubes in a tumblingbath at C. The tubes charge contains chlorotrifluoroethylene. werecharged with the 14 8 0 solution, telomer acid emul- 2a 6. In a processfor polymerizing trifiuorochloroethylsifying solution, and then Na HPOsolution in that order. ene at a temperature between 0 C. and 100 C. inthe After each charge the contents were frozen in a Dry Icepresence of apolymerization initiator and in an aqueous acetone slurry until the nextaddition. Finally the CS medium containing a dispersing agent selectedfrom the was pipetted into the mixture, and the monomer charge groupconsisting of aliphatic perfluorochloro acids and was dd d the inorganicsalts thereof, the improvement which com- At h d of 24 hours h tubes r eted a d prises adding carbon disulfide to said aqueous medium the latexwas coagulated by Dry Ice freezing, recovered, in an amount between 1and parts by weight per washed and dried. Data for these runs is set outin 100 parts of trifiuorochloroethylene and adding small T bl V,amounts, relative to the amount of said carbon disulfide,

Table V Gm. Ml 2.5% M1 5.25% M14.0% Gm. Weight Percent DSV ZST RunCF=CFC1 KgS Og Na2HPO .7HzO O8 telomer CS2 polymers, conversion as at260 soln, soln'. acid soln. gm. 0.

A.... 41.7 40.0 38. 2 46. s 25.57 61. 4 1. 339 374 41.7 40.0 38.2 46.826.16 62.6 1. 409 390 0--., 41.7 40. 0 38.2 40. s 4. 2 35. 49 85.3 1.031 231 41. 7 40.0 as. 2 46. s 4. 2 35. 48 85.0 1,036 216 41.7 40.0 38.246.8 41.7 18.05 43.0 0. 786 143 0? 0.75% solution isdichlorobenzotritluoride at 266 F.

3 ZST of a 260 C. pressing. It was noted that the addition to thepolymerization system of small amounts of Na CO or NaOCN, usually inquantities of about 0.1 by weight of the weight of carbon disulfide, orless, enhances the yield of polymer, as is indicated by Example 3.

As mentioned earlier, this invention relates to the polymerization of amono-olefin, particularly a halogenated mono-olefin which is at leasthalf fluorinated and which preferably contains from 2 to 3 carbon atoms,in an aqueous medium containing carbon disulfide and a dispersing agent,preferably an aliphatic fluorocarbon acid or salt.

Various modifications and alterations of the process of this inventionwill be apparent to those skilled in the art and may be, used withoutdeparting from the scope of this invention.

1 C telomer acid is dissolved in E20 by beating and adding KOH (pelletsand solution) until the pH is of a member of the group consisting ofsodium carbonate and sodium cyanate, at a pH of from about 8 to about11.

7. The process of claim -6 in which the member of the group consistingof sodium carbonate and sodium cyanate is added in an amount of about 10weight percent and less of the weight of carbon disulfide.

References Cited in the file of this patent UNITED STATES PATENTS2,393,157 Gleason Jan. 15, 1946 2,559,752 Berry July 10, 1951 2,640,821Pritchard et al. June 2, 1953 2,682,530 St. John June 29, 1954 2,874,152Bolstad Feb. 17, 1959 2,898,196 Buflin-gton Mar. 17, 1959

1. IN A PROCESS FOR POLYMERIZING A MONOMER CHARGE CONSISTING OF AT LEAST ONE POLYMERIZABLE FLUORINATED MONLEFIN HAVING FROM 2 TO 5 CARBON ATOMS AT A TEMPERATURE BETWEEN 0*C. AND 100*C. IN THE PRESENCE OF A POLYMERIZATION INITIATOR AND IN AN AQUEOUS MEDIUM HAVING A PH FROM M TO ABOUT 14 AND HAVING A FLUORINATED DISPERSING AGENT, THE IMPROVEMENT WHICH COMPRISES ADDING CARBON DISULFIDE TO SAID AQUEOUS MEDIUM IN AN AMOUNT BETWEEN 1 AND 50 PARTS BY WEIGHT PER 100 PARTS MONOMER CHARGE. 